1. Field of the Invention
The invention relates to a novel multi-speed wheel hub, specifically, a multi-speed wheel hub for use on vehicles travelling both off-road and on-road. More particularly, the invention relates to a novel multi-speed wheel hub having a planetary gear, a ring gear, and a shifting system including two shift rings and a piston for activating the two shift rings. The multi-speed wheel hub is suitable for use on, for example, construction vehicles, passenger cars, mass transportation vehicles, agricultural vehicles, military vehicles, trucks, tractors, logging trucks, oil field equipment, and the like.
2. Description of Related Art
There are a number of known wheel hubs currently used on automotive vehicles. One such wheel hub does not employ a planetary gear system. In this embodiment, when the vehicle is operating under a heavy load during an off-road application, all of the torque at the wheels is transmitted through the entire drive train of the vehicle, which greatly reduces the life of the drive train components. There are no other options for transmitting this torque in this device. With this alternative, it is extremely difficult to obtain smooth acceleration, particularly in off-road applications.
Moreover, this known alternative requires extreme care when pulling a heavy load because it is very easy to break a drive shaft or damage the differential due to the resultant large loads borne by these components. Some manufacturers have compensated by increasing horsepower and installing larger drive shafts, differentials, and other drive components. Manufacturers are trying to provide an axle of great strength while being able to provide the required speed. These solutions add both weight and cost to the assembly.
Another alternative employs a planetary gear system with the planetary gear system working at all times. This alternative, the full-time planetary gear alternative, is very effective for off-road applications. When operating on-road at highway speeds, however, the planet gears generate large amounts of heat because they are turning at very high speeds. As a result, very high quality gears and bearings are necessary, which results in greater manufacturing costs. Because of the great heat generated by the rotating planet gears, this full-time planetary gear alternative must be equipped with expensive cooling and lubricating systems.
There is also a third alternative disclosed in U.S. Pat. No. 5,478,290 to Buuck, et al., which is a two-speed high shift transmission. The '290 patent discloses a hydraulically controlled two-speed transmission residing primarily within a rotatable wheel hub including a hydraulically operable piston and intermediate member to control two clutches in a first planetary gear set. The first planet carrier includes a gear that drives a second planetary gear set, which results in the rotation of the wheel hub. When hydraulic pressure is applied to the piston and an intermediate member, the first clutch is engaged, which locks an inner ring gear to a stationary outer ring gear, thereby effecting a high ratio reduction. When no hydraulic pressure is applied to the piston and the intermediate member, a second clutch engages the first sun gear and the first planet carrier locking them together so that the first sun gear, first planet gear, first planet carrier, and the inner ring gear rotate in unison together thereby effecting a low ratio reduction. This alternative, however, does not allow for a direct drive ratio (1:1). Moreover, the obtainable drive ratios will not allow the vehicle to travel at the desired highway speed. Last, the two-speed high shift transmission also has a large number of parts or components, which leads to increased cost and greater opportunity for failure.
These alternatives, both of which employ planetary gear sets, generate large amounts of heat because the planet gears are always turning. Manufacturers currently compensate by using "high speed planetary axles" made from extremely accurate gears and then use an expensive cooling system for cooling the oil used to lubricate the parts. Problems are encountered because of the shorter life of the planetary gear units and the high cost of repairing them.
The difficulties suggested in the preceding are not intended to be exhaustive but are among many tending to reduce the desirability of known wheel hubs. Other noteworthy problems may exist; however, those presented above should be sufficient to demonstrate that such methods and apparatuses appearing in the past will admit to worthwhile improvement.